THE TONGUE. 



sides and under surface of the tongue it is thin and smooth, with small 

 papillae towards the tip; on the dorsum the mucous membrane is greatly 

 modified and presents characteristic appearances. The dorsal surface, more- 

 over, includes two areas, the papillary and the lymphoid, which exhibit very 

 different details. 



The papillary area comprises the anterior two thirds, the lymphoid 

 the posterior third. In the infant's tongue the junction of these areas is 

 marked by a V-shaped groove, the sulcus terminates, but this disappears 

 and later the boundary is indicated by the conspicuous row of circumvallate 

 papillae. The anterior area is everywhere beset with elevations, the papillae, 

 which are of three varieties the filiform, the fungiform and the circumval- 

 late. The filiform or conical papilla, so abundant as to impart a velvety 



Ragged free ends 

 of papilla 



Epithelium 



Tunica propria * 



Connective tissue 



Epithelium 



Blood-vessel 



Muscle-fibres 



FIG. 182. Section of lingual mucous membrane showing filiform papillae. X 75- 



appearance to the tongue, are conical or cylindrical elevations of the tunica 

 propria, composed of fibrous connective tissue with many elastic fibres and 

 covered by a thick stratum of epithelium. The surface of the connective 

 tissue core bears a number of small secondary papillae, which, however, do 

 not model the free surface of the mucous membrane. The filiform papillae 

 vary from . 5-2. 5 mm. in height and often end in brush-like strands of horny 

 epithelial cells. The fungiform papillce are far less numerous than the fili- 

 form and appear during life as red points, chiefly near the margins of the 

 tongue, in consequence of their thinner epithelium. As implied by their 

 name, they are more or less mushroom-like in form and vary from .5-1.5 mm. 

 in height. The connective tissue core is beset with a number of secondary 

 papillae, over which stretches a smooth layer of epithelium. The latter 

 contains occasional taste-buds. The circumvallate papillce, the most con- 

 spicuous of these elevations, usually number nine or ten, from six to sixteen 

 being the extremes. They are disposed as an irregular V, with the apex 

 of the group directed backwards. These elevations, from 1-1.5 mm - n 'gh 

 and from 2-3.5 mm ' broad, consist essentially of a fungiform papilla sur- 



